The present invention relates to a method for controlling an intake throttling valve for a diesel internal combustion engine, and, more particularly, relates to a novel method for controlling an intake throttling valve for a diesel internal combustion engine which is fitted with a soot catcher of a per se well known sort, so as efficiently to purge the soot catcher by operating the intake throttling valve to an appropriate amount, without running the risk of slow responsiveness, or of causing the emission of smoke and soot. The present invention also relates to apparatus for performing the above mentioned diesel internal combustion engine intake throttling valve control method.
Nowadays, it is common and conventional to provide a soot catcher to the exhaust system of a diesel internal combustion engine. Such a soot catcher catches and accumulates carbon particles and other solid particles present in the exhaust gases of the diesel internal combustion engine, and prevents their escape to the atmosphere. Since it is becoming more and more realized nowadays that such soot particles such as carbon particles may present a significant health hazard to the public, the provision of such a soot catcher is very important from the environmental and public health point of view.
Such a soot catcher normally has a filter like structure for catching the soot particles, and naturally this filter structure inevitably tends to become clogged up, over a long period of use of the soot catcher, with an accumulation of soot particles, chiefly carbon particles. When this happens, not only does the efficiency of the soot catcher for purifying the exhaust gases of the diesel internal combustion engine of soot particles contained therein drop drastically, but also the resistance of the soot catcher to the flow therethrough of exhaust gases increases, which deteriorates the actual operation of the diesel internal combustion engine, causing its breathing efficiency to drop, which causes a loss of engine power. This has presented a serious problem with regard to such a soot catcher: either it has been necessary to regularly remove the soot catcher in order to clean it, which is dirty, expensive, and troublesome; or some system has had to be provided for cleaning or purging the soot catcher in situ, without removing it from the engine.
It is possible to purge such a soot catcher by burning out the combustible soot particles such as carbon particles which are clogging the filter structure of the soot catcher by increasing the temperature of the exhaust gases passing through the soot catcher above the ignition temperature of said combustible soot particles.
During normal operation of the diesel internal combustion engine, when the load on the diesel internal combustion engine rises to a high load level wherein the excess air ratio in the exhaust gases becomes small, it is quite possible for the temperature of the exhaust gases passing through the filter structure of the soot catcher to spontaneously rise above the ignition temperature of the soot particles clogging the soot catcher, without the provision of any special means for raising the temperature of said exhaust gases. In this case, purging of the soot catcher as described above may spontaneously occur, by burning out said soot particles lodged therein as a clogging accumulation. However, this spontaneous self purging process cannot be relied upon. Diesel engines, especially in automotive vehicles, are only irregularly operated in high load conditions; and when an automotive vehicle is being operated in urban traffic it is quite unusual for the diesel internal combustion engine thereof to be operated in the high load operational region. Thus such spontaneous self purging of a soot catcher might not occur in time to purge the soot catcher before its clogging had unacceptably deteriorated the functioning of the diesel internal combustion engine to which it was fitted. Therefore it is necessary to practice some particular special and reliable method for raising the temperature of the exhaust gases of the diesel internal combustion engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof, in order reliably to purge said soot catcher whenever it becomes clogged.
A first such prior art method for raising the temperature of the exhaust gases of a diesel internal combustion engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher has been to delay the timing of fuel injection to the diesel internal combustin engine.
However, this first prior art soot catcher purging method has suffered from the disadvantage that the temperature of the exhaust gases of the diesel internal combustion engine can only be so raised when the engine is operating in a certain range of operational conditions; in other engine operational conditions the temperature of the exhaust gases does not rise up sufficiently to combust the soot particles in the soot catcher, even when fuel injection timing is delayed. Further, delaying the timing instant of fuel injection may hamper the operability of the diesel internal combustion engine, and the drivability of a vehicle to which it is fitted. Accordingly this first purging method is not of very good applicability.
A second such prior art method for raising the temperature of the exhaust gases of a diesel internal combustion engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher has been to provide a separate heater, such as an oil burner or other heating device, for heating the exhaust gas up.
However, this second prior art soot catcher purging method has suffered from disadvantages related to cost, safety, and durability. In practice this solution cannot practicably be used for a diesel internal combustion engine for use in an automotive vehicle.
A third per se well known prior art method for raising the temperature of the exhaust gases of a diesel internal combustion engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher has been to reduce the amount of excess air which is supplied to the combustion chambers of the diesel internal combustion engine, by limiting the air intake of the engine, as for example by the use of an intake throttling valve or choke valve.
A problem that has arisen with the third per se well known prior art purging method is that it is subject to the limitation that the temperature of the exhaust gases of the diesel internal combustion engine can only be so raised so as to purge the soot catcher when the engine is operating in a certain range of operational conditions; in other engine operational conditions the temperature of the exhaust gases does not rise up sufficiently to combust the soot particles in the soot catcher, even when the air intake amount of the engine is limited as by the aforesaid intake throttling valve. Further, attention must be paid to the engine operational condition, when practicing this intake throttling method for purging the soot catcher, in order not to run the risk of emission of large quantities of soot and black smoke. In other words, the amount of throttling for the intake passage which is provided by the intake throttling valve must be properly adjusted according to engine operational conditions.
Now, a particular sort of method for raising the temperature of the exhaust gases of a diesel internal combustion engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher, in which the amount of excess air which is supplied to the combustion chambers of the diesel internal combustion engine is limited by limiting the air intake of the engine by the use of an intake throttling valve has been to provide an intake throttling valve which can be positioned not only to two extreme positions but also to intermediate positions. In other words, the intake throttling valve has been controllable to any of a range of positions thereof between its fully opened (i.e. substantially non intake throttling) position and its fully closed (i.e. maximum intake throttling) position. Typically, in fact, such an intake throttling valve has been positionable to any of a continuous range of positions between said two extreme positions.
The use of such a continuously variable position intake throttling valve is very helpful with regard to securing a good and appropriate amount of intake throttling for a diesel internal combustion engine, but its control presents some difficulties. First, a typical method of controlling such a continuously variable position intake throttling valve has been to provide some means for determining a target value for the amount of opening of said intake throttling valve, said target value being determined according to the current values of various operating parameters of the diesel internal combustion engine, such as for example engine load, engine revolution speed, engine cooling water temperature, and/or the like. The actual amount of opening of the intake throttling valve is sensed by some kind of per se well known intake throttling opening amount sensor, and then the intake throttling valve is controlled by a control system so as to bring its amount of opening to be equal to said target opening value, said control by said control system being based upon a feedback process utilizing the output signal of said intake throttling opening amount sensor. In other words, the control system attempts to bring the difference between the actual amount of opening of the intake throttling valve as measured by said intake throttling opening amount sensor and the target value of opening of said intake throttling valve to zero, or approximately zero.
This sort of control, on the one hand, presents the difficulty, if the rate of movement of the intake throttling valve, i.e. the speed of bringing the opening amount of said intake throttling valve towards the target value for said opening amount, is high, that overshooting of the actual target amount for the opening amount of said intake throttling valve is likely, end thus a lot of hunting will inevitably occur. This can cause trouble with regard to the drivability and operability of the diesel internal combustion engine, and also with regard to its durability. However, such a control method has good responsiveness. On the other hand, if the rate of movement of the intake throttling valve, i.e. the speed of bringing the opening amount of said intake throttling valve towards the target value for said opening amount, is low, then, although no such problems with overshooting and/or hunting are likely, this control method can be attended with the difficulty that slowness in bringing the actual intake throttling valve opening amount to be substantially equal to the target amount for said opening amount of said intake throttling valve is likely, and thus poor responsiveness of the control system will inevitably occur. This can cause trouble with regard to emission of black smoke during operation of the diesel internal combustion engine, especially during sudden acceleration episodes of operation of the diesel internal combustion engine, in which case there is the risk of the emission of large quantities of soot and black smoke, which can be quite unacceptable with regard to the standards for quality of exhaust emissions, which are becoming more and more severe nowadays, and with regard to the safety of the public.
Therefore, a requirement has arisen for a method and apparatus for so controlling the soot purgative operation of an intake air throttling valve for a diesel internal combustion engine which will assure that the intake throttling valve is quickly and yet stably brought to its appropriate opening amount, for various operating circumstances of the diesel internal combustion engine.